Video monitors are well known in the art. Conventionally, a video monitor is coupled to equipment such as a computers and television receivers, which provide a variety of signals to the video monitor in order to obtain a display on the screen of the video monitor. One of these signals is a video composite synchronising signal (VCSS) which comprises a horizontal synchronising signal (HSS), that determines the number of horizontal lines that make up a display on a video monitor, and a vertical synchronising signal (VSS), that determines the frequency at which the display is refreshed. Conventionally, a VCSS has two levels, a first level and a second level, and by switching between these levels at particular instances in time, pulses are produced which convey both the HSS and the VSS. Also, as the duration of a HSS pulse is much shorter than the duration of a VSS pulse, the VCSS can provide the HSS while providing the VSS.
The VCSS provided by equipment that couple to video monitors may vary. For example, a VCSS provided to a video monitor may have a continuos HSS pulses when providing a VSS pulse, alternatively, a VCSS may not provide any HSS pulses when providing a VSS pulse. Generally, video monitors require a continuos sequence of HSS pulses as the absence of these pulses adversely affects timing circuits in the video monitor, thus affecting the display.
When a video monitor receives a VCSS, a conventional method of separating the VSS are extracted from the VCSS is by using an analogue circuit. While this method of separation is well known in the art, it has several disadvantages. One disadvantage is the use of analogue circuitry. Such analogue circuits conventionally utilise bipolar semiconductor devices that consume high power, and are also susceptible to degradation in performance due to variation in operational conditions. In addition, as video monitors use digital control circuitry, yet another disadvantage of this method is the need to interface the analogue circuit with the digital control circuit which limits the degree of circuit integration that may be achieved in a video monitor. Another disadvantage of this method is the delay inherent in the analogue circuitry causing loss of VCSS information. Typically, the loss may be one or more HSS pulses which adversely affects the timing circuitry. Yet another disadvantage of this method is the inability to process a VCSS that does not provide HSS pulses when providing a VSS pulse, which results in loss of information and adversely affecting the timing circuits.
Hence, a need exists for a method of processing a VCSS in a video monitor that separates the VSS without loss of information and preferably without employing analogue circuitry. In addition, the method should avoid adversely affecting timing circuits in the video monitor when a VCSS does not provide HSS pulses when providing a VSS pulse.